DE60100328T2 - Process for the extraction and purification of cyclobutanone - Google Patents

Description

Field of the invention

This invention relates to a process for the recovery and purification of cyclobutanone from a crude product mixture obtained from an oxidation product mixture resulting from the oxidation of cyclobutanol to cyclobutanone. More particularly, this invention relates to the recovery of cyclobutanone with a purity of at least 90 wt.% by a novel combination of distillation steps.

Background of the invention

Cyclobutanone is a valuable organic intermediate useful in the preparation of a variety of compounds. See, e.g., Lee-Ruff, Adv. Strain Org. Chem. (1991), 1, 167, and Bellus et al., Angew. Chem. (1988), 100(6), 820. Cyclobutanone can be prepared by the oxidation of cyclobutanol with chromium trioxide and oxalic acid in water, as described, for example, by Krumpolic and Rocek in Organic Synthesis Collective Volumes, pages 114-116. The chromium trioxide/oxalic acid oxidation is relatively unselective and produces a dilute, aqueous, crude cyclobutanone mixture containing many impurities that are difficult to separate. Typical impurities in the crude aqueous cyclobutanone include, but are not limited to, cyclopropane methanol, unreacted cyclobutanol, 3-buten-1-ol, 2-buten-1-ol, cyclopropane carboxaldehyde, cyclopropane carboxylic acid, ethers and mixed ethers of cyclobutanol, cyclopropane methanol, 3-buten-1-ol and 2-buten-1-ol, hemiketals and ketals of cyclopropane methanol, cyclobutanol, 3-buten-1-ol and 2-buten-1-ol with cyclobutanone, and other unknown compounds with boiling points higher and lower than that of cyclobutanone. Many of these impurities are color bodies and will cause the cyclobutanone product to be highly colored if not removed.

Krumpolic and Rocek, supra, describe extracting the crude cyclobutanone/water mixture with methylene chloride and drying the organic phase comprising cyclobutanone and other organic impurities over anhydrous magnesium sulfate containing anhydrous potassium carbonate. The dried organic layer is distilled twice to remove methylene chloride and recover the cyclobutanone product. The process is said to produce a relatively pure cyclobutanone product, i.e., 98-99 wt% cyclobutanone. However, from the standpoint of practical large-scale production of high purity cyclobutanone, this process suffers from many disadvantages. The extractant, methylene chloride, is quite toxic, very volatile, and is costly to handle and safely dispose of. The above-mentioned process indicates the use of about 86 kg of methylene chloride per kg of cyclobutanone produced. Accordingly, the extraction and subsequent distillation equipment required must be very large and expensive relative to the amount of cyclobutanone produced. The authors reveal that cyclobutanone is highly soluble in water and difficult to extract with high recovery rates using methylene chloride. In addition, the overall yield of cyclobutanone is low (70-80%) and the authors do not provide any methods to obtain anywhere near to remove boiling impurities such as crotonaldehyde and cyclopropanecarboxaldehyde, as well as color bodies.

French patent FR 0112261 discloses a process for the preparation of aldehydes or ketones in which molecular oxygen is used in conjunction with a bimetallic catalyst to oxidatively dehydrate primary or secondary mono- or polyfunctional alcohols containing 2 to 36 carbon atoms. The water formed is removed in the course of the reaction by azeotropic distillation using an organic solvent selected in such a way that: (1) the binary azeotrope which the solvent forms with water has a boiling point of at least 50°C, (2) the boiling point of the solvent is lower than the boiling point of the alcohol to be dehydrated, and (3) the boiling point of the solvent is lower than the boiling point of any binary azeotrope which may be formed between the alcohol and water and the alcohol and the organic solvent itself. It is specified that the organic solvent has a boiling point between 50ºC and 200ºC and is selected from aliphatic, cycloaliphatic or aromatic hydrocarbons; alkyl or alkenyl esters of aliphatic carboxylic acids, aliphatic, aromatic or cyclic ethers; aliphatic, cycloaliphatic or aromatic nitriles; aliphatic, cycloaliphatic or aromatic ketones. Furthermore, the azeotrope formed between water and the organic solvent must be heterogeneous.

Although FR 0112261 provides a general process for the azeotropic distillative dehydration of ketones, the patent states that an additional solvent must be added to perform the dehydration of the ketone. Furthermore, FR 0112261 does not consider processes for obtaining a high purity ketone product. No processes are disclosed for removing unreacted alcohol feed material, color bodies, other high and low boiling or near boiling impurities to obtain a high purity ketone product.

U.S. Patent 2,684,934 discloses a process for purifying ketones containing water and unreacted alcohol starting material, particularly for methyl ethyl ketone (MEK), methyl propyl ketone (MPK) and methyl butyl ketone (MBK) by a two or three column pressure swing distillation sequence. In the case of MEK, MPK and MBK, the composition of the ketone/water azeotrope varies significantly with moderate changes in pressure. This patent also does not contemplate methods for obtaining a high purity ketone product. No methods are disclosed for removing color bodies, other high and low boiling or near boiling impurities to obtain a high purity ketone product.

U.S. Patent 2,684,934 discloses a process for purifying mixtures of MEK and methyl isopropyl ketone containing water and unreacted ethanol and isopropanol by a combination of extractive distillation, extraction and azeotropic distillation steps with an added solvent. The crude aqueous ketone/alcohol feed is first extractively distilled with water as the extractive distillation solvent. The column base product comprising unreacted ethanol, isopropanol and water is recycled to the ketone formation step while the MEK/MIPK/water distillate product is contacted with n-hexane countercurrently in an extraction column. The water-rich raffinate containing some MIPK and MEK is returned to the extractive distillation column. The hexane-rich extract, which comprises most of the MIPK and MEK fed to the extractor and some water, is fed to an azeotropic distillation column where the remaining water is removed at the top as a heterogeneous, low boiling ternary hexane/MEK/water azeotrope. The azeotrope is allowed to phase separate, decanted, and the organically enriched layer, which contains most of the MEK and hexane, is returned to the extraction step. The aqueous layer from the decantation is returned to the extractive distillation step. MEK and MIPK are then separated in a final distillation step.

US Patent 4,186,059 describes a similar solvent-assisted azeotropic distillation and extraction process for MEK dehydration using toluene as a water entrainer in the distillation step and hydrocarbon wax as the extraction solvent. French Patent FR 78 28329 teaches similar azeotropic distillation processes for MEK dehydration using a light hydrocarbon as a water entrainer, preferably n-pentane. Soviet Patent 1,567,603 teaches the use of diisopropyl ether as a solvent for MEK dehydration.

All of these MEK-related patents teach processes that are unnecessarily complicated, expensive, and unnecessary for cyclobutanone dehydration. While MEK and water form a low boiling heterogeneous azeotrope, the liquid/liquid region is small, with high mutual solubility of MEK and water. Accordingly, MEK is not a convenient entrainer for use in its own dehydration.

Brief summary of the invention

We have developed a process for recovering cyclobutanone having a purity of at least 90 wt.% by a novel combination of distillation and processing steps. The purification process of the present invention involves a process for recovering cyclobutanone having a purity of at least 90 wt.% from a crude product mixture comprising cyclobutanone, water and a plurality of other organic compounds resulting from the oxidation of cyclobutanol in water by the steps comprising:

(1) distilling the crude product mixture to produce (i) a distillate comprising cyclobutanone, water, cyclopropane methanol, cyclobutanol, 3-buten-1-ol, 2-buten-1-ol, cyclopropanecarboxaldehyde, ethers and mixed ethers of cyclobutanol, cyclopropane methanol, 3-buten-1-ol and 2-buten-1-ol and hemiketals and ketals of cyclopropane methanol, cyclobutanol, 3-buten-1-ol and 2-buten-1-ol with cyclobutanone; and (ii) to obtain a distillation residue comprising water, metal salts and high boiling organic compounds such as γ-butyrolactone, cyclopropanecarboxylic acid and hemiketals and ketals of cyclopropanemethanol, cyclobutanol, 3-buten-1-ol and 2-buten-1-ol with cyclobutanone;

(2) allowing the resulting mixture to separate into (i) an organic phase comprising a minor amount of the cyclobutanone contained in the distillate and a major amount of impurities less soluble in water than cyclobutanone, such as ethers, ketals and color bodies; and (ii) an aqueous phase comprising water, a major amount of the Cyclobutanone contained in the distillate comprises a minor amount of more hydrophilic impurities such as alcohols and cyclopropanecarboxaldehyde;

(3) distilling the aqueous phase from step (2) to obtain (i) a minor amount of distillate comprising low boiling azeotropes comprising water and organic impurities in the aqueous phase, (ii) a major amount of distillate comprising an azeotrope of water and cyclobutanone, to obtain (iii) a distillation residue comprising water, cyclopropanecarboxylic acid, γ-butyrolactone, cyclobutanol, cyclopropanemethanol, mixed ethers of alcohols and ketals formed from the reactions between ethers and alcohols;

(4) allowing the distillate (ii) from step (3) to separate into (i) a cyclobutanone-rich organic phase comprising cyclobutanone, water and one or more aldehydes having boiling points near that of cyclobutanone, and (ii) an aqueous phase comprising cyclobutanone and water; and

(5) distilling the organic phase (i) from step (4) to obtain (i) a first distillate comprising an azeotrope of water and cyclobutanone, (ii) a second distillate comprising cyclobutanone having a purity of at least 90%, and (iii) a distillation residue comprising cyclobutanol, cyclopropanemethanol, mixed ethers of alcohols and ketals formed by reactions between ethers and alcohols.

The cyclobutanone product may contain unacceptably high levels of aldehydes, e.g., cyclopropanecarboxaldehyde and cis/trans-crotonaldehyde, since such compounds are difficult to remove in the purification process. Thus, the five-step purification process described above may include an aldehyde conversion step in which the distillations of steps (3) and/or (5) are preceded by an aldehyde conversion in which the material to be distilled in steps (3) and/or (5) is treated with a material which converts the aldehyde to another compound or compounds having boiling points higher than those of the otherwise difficult-to-separate aldehydes. This auxiliary step causes the aldehyde(s) present to be converted to products having higher boiling points and therefore easily separated from the cyclobutanone.

Another variation of the present invention provides for the addition of an external, inert (unreactive) azeotrope-forming solvent to the material distilled in step (5). Yet another variation uses a pressure differential in the distillations of steps (3) and (5).

Detailed description

In the first step of the purification process provided by the present invention, crude aqueous cyclobutanone is distilled from a crude product mixture comprising cyclobutanone, water and a plurality of other organic compounds resulting from the oxidation of cyclobutanol in water. An example of the oxidation of cyclobutanol to cyclobutanone in water is described by Krumpolic and Rocek, supra, who oxidized cyclobutanone with chromium trioxide and oxalic acid in the presence of water to cyclobutanone. This crude product mixture typically comprises about 2 to 20 wt.% cyclobutanone, about 70 to 97 wt.% water and about 0.2 to 10 wt.% Impurities including catalyst residues, unreacted cyclobutanol and a variety of by-products. The distillate from the first step comprises cyclobutanone, water, cyclopropanemethanol, cyclobutanol, 3-buten-1-ol, 2-buten-1-ol, cyclopropanecarboxaldehyde, ethers and mixed ethers of cyclobutanol, cyclopropanemethanol, 3-buten-1-ol and 2-buten-1-ol and hemiketals and ketals of cyclopropanemethanol, cyclobutanol, 3-buten-1-ol and 2-buten-1-ol with cyclobutanone. The distillation residue (undistilled material) comprises water, metal salts e.g. chromium salts resulting from the use of a chromium compound in the synthesis of the cyclobutanone, high boiling organic compounds e.g. B. γ-butyrolactone, ethers and mixed ethers of cyclobutanol, cyclopropane methanol, 3-buten-1-ol and 2-buten-1-ol and hemiketals and ketals of cyclopropane methanol, cyclobutanol and heavy acids, e.g. oxalic acid and cyclopropanecarboxylic acid.

The first step is carried out by heating the crude oxidation mixture to its boiling point, followed by collection and condensation of evolved vapors. It is desirable that the first distillation step remove substantially all of the cyclobutanone in the crude reaction mixture and effect concentration of the cyclobutanone in the vapor condensate. Many of the organic impurities present in the crude product mixture form low boiling azeotropes with water and tend to be carried to the distillation head with the cyclobutanone during the first distillation step. A number of these impurities are highly colored and will cause coloration of the final cyclobutanone product if not effectively removed. However, we have found that these impurities are generally much less soluble in water than in cyclobutanone. Although the cyclobutanone/water binary system separates into two liquid phases at concentrations above 20 wt% cyclobutanone, due to the presence of hydrophobic impurities, a typical crude cyclobutanone condensate from the distillation of step (1) separates into two liquid phases at much lower concentrations of cyclobutanone, e.g. as low as about 1 to 2 wt% cyclobutanone. Most of the cyclobutanone is present in the aqueous layer, whereas the more hydrophobic impurities tend to concentrate in the organic layer. In this way, many of the heavy impurities can be easily removed from the crude aqueous cyclobutanone mixture prior to further distillation while still maintaining a high recovery of cyclobutanone.

The concentration of cyclobutanone in the condensed distillate from step (1) is typically in the range of 2 to 20 wt.%, preferably 4 to 12 wt.%, based on the total weight of the condensed distillate. This concentration range maximizes the recovery of cyclobutanone in the aqueous phase while minimizing co-extraction of impurities. If necessary, the concentration of cyclobutanone in the condensed distillate can be adjusted to 2 to 20 wt.%, preferably 4 to 12 wt.%, by the addition of fresh water. Generally, one or more equilibrium separation stages are sufficient to achieve the desired concentration in the flash distillation step.

The organic and the aqueous phase formed during the condensation of the distillate from the first step are separated and the aqueous layer is kept for subsequent distillative purification steps. The organic layer can be further purified with fresh water either in Cross-current or multi-stage counter-current extraction mode to extract additional cyclobutanone from the undesirable impurities, improving the recovery rate. Typically 1 to 8 stages, more preferably 2 to 6 stages of cross-current or counter-current extraction are sufficient to recover most of the cyclobutanone from the organic phase. The preferred water to organic phase weight ratio is in the range of 1:4 to 5:1, more preferably 0.5:1 to 2:1. All aqueous extract phases from each extraction step are combined with the aqueous layer from distillation step (1) for subsequent recovery and purification of cyclobutanone. The raffinate phase, which contains major organic impurities, is discarded as a waste stream.

The aqueous layer from the flash distillation step is further processed in a two-stage azeotropic distillation sequence with an intermediate decantation step, i.e., steps (3), (4) and (5) described above. This distillation sequence serves to remove water, alcohols, high and low boilers and can produce cyclobutanone with a purity equal to or greater than 90 wt.%, preferably greater than 95 wt.%, more preferably greater than 99 wt.%. Cyclobutanone itself is used as a dehydrating agent to remove water from the mixture. The two-column sequence can be operated in a batch or continuous manner with equal effectiveness.

In the third step of our new purification process, the aqueous phase from the first distillation step is introduced into a first still and distilled to first yield a smaller amount of distillate which is collected to remove low boiling compounds and low boiling organic/water azeotropes. The foreshot is typically 0.1 to 0.6 wt%, more typically 0.1 to 0.3 wt% of the initial feed to the still. The head temperature when the foreshot is collected is typically 2 to 4ºC less than the boiling point of the cyclobutanone/water azeotrope. The actual head temperature will of course depend on the operating pressure of the column. For example, at 740 Torr, the head temperature is about 78 to 81ºC.

When the distillation column overhead temperature of step (3) approaches, i.e., is less than about 2°C from, the boiling point of the cyclobutanone/water azeotrope, collection of the product fraction, i.e., distillate (ii) of step (3), is commenced. The composition of the product fraction is substantially that of the water/cyclobutanone azeotrope, i.e., about 80% by weight cyclobutanone. Collection of this product fraction is continued until the cyclobutanone is substantially removed from the still. While the cyclobutanone/water azeotrope is distilling off in the overhead, the distillation column overhead temperature remains substantially constant at the boiling point of the cyclobutanone/water azeotrope. For example, at about 740 torr column pressure, the overhead temperature is about 82 to 83°C. If distillation is continued after the overhead temperature has risen significantly above that of the cyclobutanone/water azeotrope, the higher boiling impurities, e.g. cyclobutanol and cyclopropanemethanol, and substantial amounts of water will distill off at the overhead and contaminate the distillate product fraction. It is preferred that distillation be terminated after the temperature has risen to 1 but not more than 15°C, more preferably 2 but not more than 8ºC, and most preferably 2 to not more than 5ºC above the boiling point of the cyclobutanone/water azeotrope at the column operating pressure.

The distillation residue (iii) from step (3) typically contains high boiling impurities such as cyclopropanecarboxylic acid, γ-butyrolactone, cyclobutanol, cyclopropanemethanol, mixed ethers of alcohols and ketals formed from reactions between ethers and alcohols, and any remaining cyclobutanone. It is advantageous to operate the first azeotropic distillation step in a column with sufficient equilibrium stages and sufficient reflux to substantially separate the alcohol/water azeotropes from the cyclobutanone/water azeotrope. If these impurities are allowed to co-distill with the cyclobutanone, they tend to accumulate in the bottom of the second distillation column. High concentrations of alcohols, e.g. B. Cyclobutanol and cyclopropane methanol, at the bottom of the second column promote losses of cyclobutanone to hemiketals and ketals and also lead to water evolution. Stringent water specifications for the product cyclobutanone are then difficult to meet. The column should contain at least five equilibrium stages, more preferably at least 10 equilibrium stages if the cyclobutanol and cyclopropane methanol concentrations in the column feed are low, i.e. less than 0.005 wt.%. The column should contain at least 10 equilibrium stages, more preferably at least 15 equilibrium stages if the cyclobutanol and cyclopropane methanol concentrations in the column feed are high, i.e. greater than 0.005 wt.%. The preferred reflux ratio will, of course, depend on the number of equilibrium stages and the concentration of the alcohols, but a ratio of 2:1 to 10:1, preferably 2:1 to 7:1, is usually sufficient. The distillation may be carried out at a constant reflux ratio throughout or may be operated with a variable reflux practice in a manner well known in the art. If sufficient stages and a sufficient reflux ratio are provided, most of the alcohols and other heavy impurities can be effectively separated and left with the water remaining in the still. Typical operating pressures are 100 to 200 Torr (0.013 to 0.4 MPa), preferably 380 to 1520 Torr (0.05 to 0.2 MPa).

Step (3) has been described above in the context of a batch operation. However, it will be apparent to those skilled in the art that step (3) can be carried out in continuous mode, wherein the distillates (1) and (ii) and the residue (iii) are simultaneously removed from a distillation column. For example, continuous operation of step (3) can comprise feeding the aqueous phase from step (2) to a distillation column and removing from the column (i) a minor amount of distillate, e.g. from the side of the upper section of the column, comprising low boiling azeotropes comprising water and organic impurities in the aqueous phase, (ii) a major amount of distillate, e.g. from the top or an upper section of the column, comprising an azeotrope of water and cyclobutanone, and (iii) a column underflow product, e.g. B. a liquid distillation residue removed from the bottom of the column and comprising water, cyclopropanecarboxylic acid, γ-butyrolactone, cyclobutanol, cyclopropanemethanol, mixed ethers of alcohols and ketals formed from reactions between ethers and alcohols.

If sufficient stages and a sufficient reflux ratio are provided so that the composition of the product fraction is essentially that of the cyclobutanone/water azeotrope, the product fraction readily separates into two liquid phases. The upper organic phase, i.e., phase (i) of step (4), which contains about 96 wt.% cyclobutanone, about 4 wt.% water, and less than about 1 to 2 wt.% organic impurities, is subjected to further processing in step (5). The lower water phase, i.e., phase (ii) of step (4), which contains about 20 wt.% cyclobutanone, may be recycled to subsequent distillations of step (3) to increase the overall cyclobutanone recovery, or it may be discarded, as desired. It is preferable to recycle the aqueous layer.

Step (5) of our new process involves distilling the organic phase (i) from step (4) to obtain cyclobutanone having a purity of at least 99%, preferably at least 99.5%. In step (5) a first distillate fraction is collected at a column head temperature of about that of the boiling point of the cyclobutanone/water azeotrope. For example, at about 740 Torr column pressure the head temperature is about 82-83°C. The composition of the first distillate fraction is essentially that of the water/cyclobutanone azeotrope (about 80 wt% cyclobutanone). The first distillate fraction separates into two liquid phases upon standing. The aqueous layer can be recycled to step (3) and the organic layer to step (5). The collection of the first distillate fraction is continued until water is substantially removed from the material fed to the still, e.g., water is removed until the material fed to the still contains less than about 1 wt.%, preferably less than 0.4 wt.%, preferably less than 0.3 wt.% water. As the water content of the material being distilled falls below the composition of the cyclobutanone/water azeotrope, the column top temperature gradually increases to the boiling point of pure cyclobutanone, i.e., 98-99°C at 760 torr.

When the column head temperature approaches the boiling point of pure cyclobutanone, i.e., less than about 1ºC, collection of the product fraction is begun. The composition of the product fraction is essentially that of pure cyclobutanone. While the cyclobutanone product is distilled off in the head, the head temperature of the distillation apparatus remains essentially constant at the boiling point of pure cyclobutanone. For example, at a column pressure of 740 torr, the head temperature is 96 to 97ºC. If distillation is continued after the head temperature has risen significantly above that of pure cyclobutanone, the higher boiling impurities, e.g., cyclobutanol, cyclopropane methanol, ketals and ethers, are carried into the head and contaminate the distillate product fraction. It is preferable to terminate the distillation after the head temperature has risen 0.1 but not more than 6ºC, more preferably 0.2 but not more than 4ºC, and most preferably 0.2 but not more than 2.5ºC above the boiling point of the pure cyclobutanone at the column operating pressure.

The distillation column of step (5) should contain at least 8 equilibrium stages, preferably at least 12 equilibrium stages. The preferred reflux ratio will of course depend on the number of equilibrium stages, but a ratio of 2:1 to 12:1, preferably 2:1 to 8:1, is generally sufficient. The distillation can be carried out at a constant reflux ratio throughout. or operated with variable reflux practices in a manner well known in the art. Typical operating pressures are 100 to 3000 torr (0.013 to 0.4 MPa). More typical pressures are 380 to 1520 torr (0.05 to 0.2 MPa). If sufficient stages and reflux ratio are provided and other aspects of this invention are followed, cyclobutanone product purities of greater than 90 wt.%, more typically greater than 95 wt.%, and most preferably greater than 99 wt.% are readily achievable.

The residue in the pot typically includes unrecovered cyclobutanone as well as high boiling impurities such as cyclopropanecarboxylic acid, γ-butyrolactone, cyclobutanol, cyclopropanemethanol, mixed ethers of alcohols and ketals formed from reactions between ethers and alcohols. We have found it advantageous to recycle the pot residue from step (5) to subsequent distillations of step (3) rather than feeding it to subsequent distillations of step (5). In this way, cyclobutanol and cyclopropanemethanol are not allowed to accumulate to significant concentrations in the pot of the distillation of step (5), i.e., more than 2 to 3 wt.%. High concentrations of alcohols in the dewatering environment at the bottom of the second column promote losses of cyclobutanone to hemiketals and ketals and lead to water evolution. High recovery and stringent water specifications for the product cyclobutanone are then difficult to meet. The separation of the alcohols from cyclobutanone is best carried out in the presence of large excesses of water, i.e. in the distillation of step (3), to shift the hemiketal/ketal equilibrium towards cyclobutane/alcohol instead of ketal.

Although the process provided by the present invention is described in detail herein as a batch operation, it will be apparent to those skilled in the art that it may be operated in a continuous mode.

When aldehyde concentrations in the organic phase (i) of step (4) are above the desired purity specification of the cyclobutanone product, removal of some or all of such aldehydes is required prior to the distillation of step (5). Typically, the aldehyde content of the cyclobutanone product should be less than 2 wt.%, preferably less than 0.5 wt.%, more preferably less than 0.2 wt.%. Aldehydes that are particularly difficult to separate by distillation are cyclopropanecarboxaldehyde and cis/trans-crotonaldehyde. These aldehydes boil within a few degrees of cyclobutanone and are extremely difficult to remove economically by distillation. Accordingly, it is desirable to remove them by other means. The preferred means is via chemical conversion to high boiling species that are easily separated by distillation. We have discovered that near-boiling aldehyde impurities can be converted to high-boiling, easily distilled compounds by oxidation with molecular oxygen or a molecular oxygen-containing gas, such as air, or by condensation reactions catalyzed by amines or inorganic bases.

The near boiling aldehyde impurities can be easily converted to high boiling acids under mild conditions by contacting the organic phase (i) of step (4) with a molecular oxygen-containing gas such as oxygen, air or oxygen-enriched air. Thus, molecular oxygen or air can be bubbled through the mixture containing the aldehyde and held at an oxidation temperature for a given contact time. Typical conditions for oxidation are 4 to 120 hours hold time at 20 to 80ºC, more typically 15 to 60 hours at 40 to 60ºC. The oxidation reaction is highly selective for the oxidation of the aldehyde and losses of the ketone are normally significantly less than 1% of the initial feed.

It is well known in the art that other oxidants, e.g. peroxidants, convert aldehydes to acid, but we have found that these compounds are detrimental in our invention. Peroxyacids such as peracetic acid are not preferred because they are nonselective and destroy large amounts of the cyclobutanone along with the aldehydes. Although aldehydes are highly reactive toward peroxyacids, in the presence of the large excess of cyclobutanone over the aldehydes, the formation of the lactone γ-butyrolactone tends to prevail over the formation of acids from the aldehydes. For similar reasons, hydrogen peroxide or organic hydroperoxides such as tert-butyl hydroperoxide are not preferred.

A second method for converting the aldehydes into readily distillable compounds takes place via base-catalyzed aldol-type condensation reactions. A catalytic amount of base, e.g. 0.1 to 1 stoichiometric equivalent based on the amount of aldehyde present, is added to the organic phase (i) of step (4). The aldehyde-containing mixture is heated and maintained at temperature for a given period of time. Typical conditions for the condensation reaction are a reaction time of 2 to 75 hours at 20 to 80°C, more typically 15 to 50 hours at 40 to 60°C. During the reaction period, the more reactive aldehydes are converted to higher boiling condensation products, while only a small fraction of the cyclobutanone participates in similar condensation reactions.

Preferred bases are secondary and tertiary amines, inorganic bases and basic resins, especially those with secondary amine functionality. Weaker bases, although they reduce the reaction rate, are more selective for aldehyde over ketone condensation and are accordingly preferred. The preferred bases have a pKa of less than 11, preferably less than 10.5. The preferred secondary and tertiary amines include di- and trialkylamines in which the alkyl groups are selected from alkyl containing 1 to 20, preferably 2 to 10, carbon atoms and hydroxyalkyl groups containing 2 to 4 carbon atoms. A particularly preferred base is diethanolamine. Primary amines such as n-butylamine are not preferred because they are nonselective and destroy a large fraction of cyclobutanone along with the aldehydes. Although aldehydes are highly reactive toward base-catalyzed condensation reactions, in the presence of large excess of cyclobutanone over the aldehydes, the formation of the ketone-derived imine tends to predominate over the formation of the aldol condensation products of the aldehydes.

Since the base acts as a catalyst and not as a reagent, the base continues to catalyze condensation reactions, particularly the undesirable cyclobutanone condensation reaction, during the final distillation step. This tendency to further catalyze the cyclobutanone condensation, is particularly pronounced at the high temperatures and dry environment of the distillation reboiler or still. Accordingly, it is critical for high yields of cyclobutanone to either remove or neutralize the base prior to the final distillation step or to remove it rapidly during the second distillation. If the base catalyst boils lower than the cyclobutanone/water azeotrope or forms an azeotrope with water having a boiling point below that of the cyclobutanone/water azeotrope, the base can be rapidly removed from the still in step (5), e.g., as part of the first distillate (i) of step (5). For example, diisopropylamine forms a minimum boiling azeotrope with water having a boiling point of 74°C and therefore can be removed via distillation as a component of the first distillate (i) of step (5). The amount of first distillate comprising an azeotrope of low boiling amine and water is typically 0.2 to 3.0 wt.%, more typically 0.5 to 2.0 wt.% of the material distilled in step (5). The column overhead temperature is typically near the boiling point of the amine/water azeotrope while the light ends are collected. The actual overhead temperature will, of course, depend on the operating pressure of the column. For example, at 740 torr the overhead temperature is about 73 to 74°C with diisopropylamine as the base catalyst. It is preferred that the boiling point of the amine or amine/water azeotrope be at least 8°C, more preferably at least 15°C less than the boiling point of the cyclobutanone/water azeotrope.

The base catalyst, particularly higher boiling bases that cannot be removed by distillation, can be neutralized by adding acid, but accurate titration is difficult. Using too little acid for complete neutralization does not improve the catalytic action of the remaining base, while using too much acid promotes an undesirable acid-catalyzed ketal and ether formation reaction in the following final distillation step. We have discovered that the base can be effectively removed from the cyclobutanone mixture by treatment with a resin in the form of a strong acid, e.g., an acidic ion exchange resin bearing sulfonic acid groups. The acidic resin can be contacted with the base-containing mixture either as a slurry of the resin powder or in a packed bed of the resin. When the resin is slurried, it can be recovered from the mixture by filtration methods known in the art. A preferred acidic resin is the hydrogen form of Amberlyst 15 resin. Many other resins with similar configuration work effectively for base removal.

A high boiling solvent (Solvent I) may optionally be added to the feed of distillation step (5) to provide a foot or residue of the distillation to improve heat transfer and cyclobutanone recovery. This Solvent I should have the following properties: (1) a boiling point significantly above, e.g., at least 30°C, the boiling point of cyclobutanone; (2) does not form a binary azeotrope with cyclobutanone; (3) does not form a binary azeotrope with alcohol impurities that has a boiling point close to the boiling point of pure cyclobutanone, e.g., within 10°C; and (4) does not react with cyclobutanone. Examples of such high-boiling, inert solvents I are high-boiling straight and branched chain alkanes and alkyl esters of alkanoic acids, such as n-decane, n-nonane and isobutyl isobutyrate.

Mixed solvents having these properties are also useful for this aspect of the invention. The inert cosolvents I typically have a boiling point of at least 130°C, preferably 140 to 200°C. The amount of optional high boiling solvent I that can be used is typically in the range of 0.1 to 2 parts by weight based on the weight of the feed material for the distillation of step (5).

Another variant of the process provided by the present invention uses an external solvent (solvent II) in step (5). The external solvent II is selected to provide a ternary system consisting of cyclobutanone, water and the external solvent II and having the following features:

(1) The solvent forms a heterogeneous, minimum boiling binary azeotrope with water or a heterogeneous, ternary, minimum boiling azeotrope with water and cyclobutanone which is the lowest boiling of all binary azeotropes and pure components in the ternary system; and

(2) The solvent does not react with cyclobutanone.

The inert foreign solvent II preferably does not form a binary azeotrope with alcohol impurities, which has a boiling point close to the boiling point of pure cyclobutanone, i.e. within 10°C. The organic solvent II is preferably selected from aliphatic, cycloaliphatic and aromatic hydrocarbons containing up to 7 carbon atoms; aliphatic, aromatic and cyclic ethers containing up to 6 carbon atoms; aliphatic and cycloaliphatic nitriles containing up to 5 carbon atoms; and aliphatic and cycloaliphatic ketones containing up to 6 carbon atoms; aliphatic and cycloaliphatic halogenated hydrocarbons containing up to 6 carbons and up to 3 chlorine or 6 fluorine or 3 bromine atoms; and aliphatic or cycloaliphatic esters containing up to 5 carbon atoms. Specific examples of the inert added solvent II include methyl tert-butyl ether (MTBE), tert-amyl ether, ethyl acetate, isopropyl acetate, n-pentane, n-hexane, cyclohexane, methyl isopropyl ketone, 1-chlorobutane and 2-chlorobutane.

When the inert organic foreign solvent II is used in the distillation step (5), a first distillate fraction is collected at a column head temperature of about that of the boiling point of the binary solvent II/water azeotrope or the ternary solvent II/water/cyclobutanone azeotrope. For example, with MTBE as solvent II and a column pressure of about 740 torr, the head temperature is about 51-52°C. The composition of the first distillate (i) essentially comprises the binary or ternary azeotrope with solvent II. The first distillate (i) separates into two liquid phases upon standing. The aqueous phase can be recycled to subsequent distillations of step (3) and the organic phase to subsequent distillations of step (5). Collection of the first distillate (i) is continued until substantially all of the water is removed from the still. When the water content of the distillation apparatus falls below the composition of the binary or ternary azeotrope with the solvent, the head temperature gradually increases to the boiling point of the added solvent II. The next distillation fraction, which contains water, cyclobutanone and solvent II is removed when the last traces of water and any excess solvent II are distilled off at the top. This fraction can also be recycled to subsequent distillations of step (3). When the column temperature closely approaches the boiling point of pure cyclobutanone, ie less than about 1ºC away from it, collection of product fraction (ii) is started as described above.

The amount of inert foreign solvent II added to the feed material distilled in step (5) is based on the water content of the feed material. Typically, sufficient solvent II is introduced into the still to give an excess, preferably a 5-30% excess, over the composition of the binary solvent II/water azeotrope or the ternary water/solvent II/cyclobutanone azeotrope. For example, when MTBE is used as solvent II, the composition of the binary MTBE/water azeotrope is 4 wt% water. Thus, MTBE is added at a rate of at least 24 kg MTBE per kg water in the feed, more typically 25.2 to 36 kg MTBE per kg water.

In yet another variation of our invention, the distillations of step (3) and step (5) are carried out using different pressures. In this embodiment of our invention, described herein as operating in continuous feed mode, the separation operation specified above in step (4) is not essential to the successful operation of the overall process for recovering cyclobutanone having a purity of 90% or more. However, the separation of step (4) can be included in the operation of the process. This embodiment of our invention thus consists of a process for recovering cyclobutanone having a purity of at least 90% by weight from a crude product mixture comprising cyclobutanone, water and a plurality of other organic compounds resulting from the oxidation of cyclobutanol in water by the steps comprising:

I. Distilling the crude product mixture to produce (i) a distillate comprising cyclobutanone, water, cyclopropane methanol, cyclobutanol, 3-buten-1-ol, 2-buten-1-ol, cyclopropanecarboxaldehyde, ethers and mixed ethers of cyclobutanol, cyclopropane methanol, 3-buten-1-ol and 2-buten-1-ol and hemiketals and ketals of cyclopropane methanol, cyclobutanol, 3-buten-1-ol and 2-buten-1-ol with cyclobutanone; and (ii) to obtain a distillation residue comprising water, metal salts and high boiling organic compounds such as γ-butyrolactone, cyclopropanecarboxylic acid and hemiketals and ketals of cyclopropanemethanol, cyclobutanol, 3-buten-1-ol and 2-buten-1-ol with cyclobutanone;

II. Allowing the resulting mixture to separate into (i) an organic phase comprising a minor amount of cyclobutanone contained in the distillate, a major amount of impurities less soluble in water than cyclobutanone, such as ethers, ketals and color bodies; and (iii) an aqueous phase comprising water, a major amount of the cyclobutanone contained in the distillate, a minor amount of more hydrophilic impurities, such as alcohols and cyclopropanecarboxaldehyde;

III. Distilling the aqueous phase from step II at a pressure in the range of 100 to 2000 Torr to obtain (i) a condensed distillate product which is an azeotrope of water and cyclobutanone, and (ii) obtaining a column underflow product comprising water, cyclopropanecarboxylic acid, γ-butyrolactone, cyclobutanol, cyclopropanemethanol, mixed ethers of alcohols and ketals formed from reactions between ethers and alcohols; and

IV. distilling the distillate (i) from step III at a pressure of 2000 to 6000 torr to obtain (i) a distillate product comprising an azeotrope of water and cyclobutanone which is recycled to the feed to the distillation of step III and (ii) a column underflow product comprising cyclobutanone having a purity of at least 90%;

provided that the distillation of step IV is operated at a pressure at least 760 torr higher than the pressure at which step III is operated.

Distillation step III is operated at a pressure of 100 to 2000 Torr (0.013 to 0.26 MPa), preferably 700 to 1250 Torr (0.093 to 0.17 MPa). The condensed distillation product from the distillation of step III, optionally after destruction of nearby boiling aldehydes, is fed to the distillation column of step IV for the final purification of the cyclobutanone at a higher pressure than that of the distillation of step III. The distillation column of step IV is operated at a pressure substantially above, e.g. at least 760 Torr (0.1 MPa), more preferably at least 2280 Torr (0.3 MPa) the pressure of the distillation column of step III. The distillation column of step N is typically operated at pressures of 2000 to 6000 torr (0.26 to 0.8 MPa), more typically at pressures of 3500 to 5500 torr (0.4 to 0.53 MPa). If sufficient stages and a sufficient reflux ratio are provided and other aspects of this invention are followed, cyclobutanone product purities of greater than 90 wt.%, more typically greater than 95 wt.%, and most preferably greater than 99 wt.% are readily achievable.

Our new process is further illustrated by the following examples. The percentages given in these examples are by weight unless otherwise stated.

Production of crude cyclobutanone product

A 50 L glass round bottom flask was fitted with an electric heating mantle, an air driven stirrer motor, and a thermocouple. One neck of the flask was fitted with a short, 0.61 meter (2 ft) unpacked glass column, a distillation head, a water cooled condenser, and was connected to a 5 L drop bottom receiving flask. Both the receiving and reaction flasks were placed under nitrogen and fitted with a dry ice vent trap. The reaction flask was charged with 5750 g of water. The air driven stirrer was started, and 1315 g of concentrated hydrochloric acid and 1140 g of cyclopropane methanol were added to the flask. The mixture was heated to reflux and held at that temperature for 4 hours. The mixture was cooled to 30ºC and transferred to an ice-cooled 50 L jacketed round bottom flask equipped with an air-driven stirrer motor, thermocouple, nitrogen purge line and dry ice vent condenser. With stirring, 0.9 L of water was added to the ice-cooled flask followed by 3961 g of oxalic acid. The reaction was allowed to cool to 25ºC and a mixture of 3148 g of chromium trioxide in 4860 g of water was added. was added dropwise to the jacketed flask over a period of 10 hours while maintaining the temperature at 25°C. After completion of the addition of the aqueous chromium trioxide, the reaction mixture was stirred at 25°C for 1 hour.

EXAMPLE 1- Step (1)-Distillation

The crude cyclobutanone product prepared as above was transferred to a 50 L round bottom distillation flask and heated to boiling point. Over the course of 24 hours of operation at total withdrawal, approximately 3881 g of distillate product of step (1) was collected in the collector. The material of step (1) in the collector separated into two liquid phases. The small, highly colored upper organic phase (i) comprised approximately 50% cyclobutanone. The crude aqueous phase (ii) comprised 8.8% cyclobutanone. Accordingly, no water addition was required to adjust the cyclobutanone concentration to the preferred range. Although variations are possible, the concentration of cyclobutanone in the aqueous layer (ii) is typically 3 to 20% of the solution, more typically 6 to 15%. The organic layer (i) can contain up to 95% cyclobutanone, more typically 30 to 85% cyclobutanone.

EXAMPLE 2 - Step (2)-Water extraction of the organic phase (i) of the distillate from step (1)

Cross-flow extraction experiments were performed on the organic phase (i) obtained from the step (1) distillation described above to demonstrate that: (1) further cyclobutanone can be recovered from the organic phase (i) and (2) water is a selective solvent for the separation of cyclobutanone from other oxidation byproducts. The organic phase (i) consisted of approximately 5% water, 59% cyclobutanone and 36% organic impurities.

A series of cross-flow extraction experiments were carried out on a portion of the small organic phase layer (i) obtained from the step (1) distillation using the following procedure. The organic phase (1) was introduced into a separatory funnel together with an equal mass of demineralized water. The funnel was shaken for 2 minutes and the phases were allowed to separate. The resulting aqueous and organic phases were decanted and each phase was analyzed by GC. The new organic phase thus obtained from the first extraction was then again combined with an equal mass of fresh demineralized water for the second extraction and so on for a total of 8 cross-flow extractions. Since it was not possible to identify all impurities individually, a response factor of 1 for the conductivity (TC) detector was assumed for the impurities and the weight percentages for water, cyclobutanone and impurities were normalized to 100%.

The phase compositions and partition coefficients for the series of 8 cross-flow extractions are given in Table I, where the weights of the organic (or raffinate) phase and the aqueous (or extract) phase are given in grams, CBON is cyclobutanone, Imp represents the impurities present, and the values given for organic and aqueous phase composition and cumulative recoveries are weight percentages. The partition coefficient is expressed as the mass fraction of a given component in the water (extract) phase divided by the mass fraction of the same component in the organic (raffinate) phase. After eight extractions, 78% of the cyclobutanone and only 19% of the impurities in the original organic layer were recovered in the combined extract streams. Even higher recovery of cyclobutanone is possible when larger amounts of water and more extraction stages are used. The partition coefficient for cyclobutanone is typically an order of magnitude higher than that of the impurities, thus demonstrating that water is a very selective extraction solvent for cyclobutanone over the impurities. TABLE I

EXAMPLE 3 - Step (3) distillation

About 789 kg (1740 pounds) of the aqueous phase (ii) prepared by the step (1) distillation procedure described above was introduced into a 500 gallon (3.8 L) glass-lined reactor equipped with a 6.1 m x 25.4 cm diameter (20 feet x 10 inch diameter) packed column, a reflux divider, a condenser and a receiving vessel. The composition of the initial feed was about 9% cyclobutanone and 0.25% cyclopropanecarboxaldehyde. The reactor vessel was heated with steam and maintained at total reflux until the column head temperature reached about 80°C. The reflux ratio was switched to 6:1 to begin collection of distillate fractions. At a head temperature between 81.2-82ºC, a small distillate foreshot was collected to remove low boilers from the system. The foreshot weighed about 2.9 kg (6.39 lbs) or 0.4% of the initial feed and comprised about 1.9 kg (4.13 lbs) of cyclobutanone. The product fraction was collected at a reflux ratio of 6/1 at a column head temperature between 81.9-85ºC. The product fraction weighed 81.6 kg (180 lbs) and contained 78.5% cyclobutanone, approximately the composition of the cyclobutanone/water azeotrope, and 0.35% cyclopropanecarboxaldehyde. The vessel was cooled and 703.3 kg (1548.5 pounds) of material containing 0.4% cyclobutanone was discharged from the still. Cyclobutanone recovery was 97% of the feed charge at 95% recovery. This experiment clearly demonstrates that cyclobutanone can be easily concentrated to the azeotropic composition, but that cyclobutanone cannot be efficiently fractionated from cyclopropanecarboxaldehyde.

EXAMPLE 4 - Step (4) Separation

The product fraction of the step (3) distillation described above was allowed to separate into two liquid phases. The lower aqueous layer [aqueous phase (ii)], weighing 19.5 kg (43 lbs) and containing 18% cyclobutanone, was drained from the receiver and saved for recycle. The upper organic layer [organic phase (i)], weighing 62.1 kg (137 lbs) and containing 94.5% cyclobutanone and 0.35% cyclopropanecarboxaldehyde, was saved for further purification.

EXAMPLE 5 - Step (5) distillation

Approximately 64.6 kg (142.5 pounds) of the organic phase (i), prepared according to the procedures described above, was introduced into a 100 L glass still equipped with a 1.37 m x 15.2 cm (54 in. x 6 in.) diameter column packed with 6.35 mm (2.5 in.) HC-276 Penn State random packing, a reflux splitter, a condenser, and receivers. The feed was not treated with the optional aldehyde destruction step. The still was heated with steam and maintained at total reflux until the head temperature reached about 81.7°C. The reflux ratio was switched to 6/1 to begin collection of the first distillate fraction. As the cyclobutanone/water azeotrope distilled from the bubble, the head temperature remained constant at about 82ºC. As the water content in the column fell below the azeotropic composition, the temperature began to rise rapidly, leveling off at about 98ºC. This fraction [first distillate (i)] weighed 22.7 kg (50 pounds) of material containing 80% cyclobutanone. It was saved for recycling in subsequent Step 3 distillations.

At this point in the Step 5 distillation, the water was essentially removed from the distillation apparatus and product collection began. Distillation was continued until the bottom jacket temperature reached 143ºC and the head temperature was near 90ºC. A total of about 30.8 kg (68 pounds) of product fraction [second distillate (ii)] was collected. The product fraction contained 99.17% cyclobutanone, 0.15% water, 0.57% cyclopropanecarboxaldehyde, 0.04% butyrolactone with no detectable cyclopropanemethanol or cyclobutanol. The still bottoms [still bottoms (ii)] weighed 8.4 kg (18.4 lbs) and comprised about 0.3% cyclopropane methanol, 0.04% water and about 5% unidentified heavy residues. This material was saved for recycling to the step (3) distillation.

EXAMPLE 6 - Step (3) distillation

An aqueous mixture containing 13.2% cyclobutanone and 0.7% cyclobutanol obtained by the step (1) distillation and step (2) separation described in Examples 1 and 2 was introduced into a 2 L glass round bottom flask equipped with a vacuum-jacketed 20-plate Oldershaw column with an inner diameter of 2.5 cm (1 inch), a liquid divider head, a reflux timer and a cooling water condenser. The column was operated in batch mode at a reflux ratio of 6/1. About 0.2% of the still feed was collected at a column head temperature of 79-80°C as distillate (i) comprising low boilers, water and some cyclobutanone. The major product fraction [distillate (ii)] was collected at a head temperature between 81.1ºC and 85ºC. The distillate (ii) separated into two liquid phases with an overall composition of about 80% cyclobutanone, 20% water and less than 0.1% cyclobutanol. A final distillate fraction collected at a head temperature greater than 85ºC contained high concentrations of cyclobutanol, e.g. greater than 2%, and was kept separate from the major product fraction. The still bottoms [distillation bottoms (iii)] were found to contain 0.9% cyclobutanol and less than 1% cyclobutanone. The overall recovery of cyclobutanone in the major product fraction was 92%. This example demonstrates that cyclobutanol can be effectively separated from cyclobutanone by carefully controlling the separation stages, reflux ratio and column head temperature.

EXAMPLE 7 - Step (4) Separation

The major product fractions from several step (3) distillations performed as in Example 6 were poured into a 500 mL separatory funnel. The total mass was 346.65 g. The mixture was allowed to separate into phases. The lower water phase (68.6 g), comprising about 21% cyclobutanone, was decanted and saved for recycle. The upper organic phase (265.3 g) comprised about 92% cyclobutanone and 7.0% water.

EXAMPLE 8 Step (5) distillation

A portion, 254.5 g, of the organic layer obtained in Example 7 was introduced into the still of a batch distillation apparatus. The distillation apparatus comprised a 500 mL round bottom flask connected to a 2.5 cm (1 inch) inner diameter vacuum-jacketed glass column equipped with a liquid divider head, reflux timer, cooling water condenser, distillate receiver flask, nitrogen line, and dry ice trap. The column was packed with 1 m (40 inches) of 3.2 mm Penn State packing. After equilibrium at total reflux was reached, the reflux timer was set to 16% withdrawal and product collection began. An initial distillate fraction [first distillate (i)] consisting of 62.4 g of material was collected while the distillation head temperature remained constant at about 82°C. This material separated into two liquid phases in the receiver flask and was found by gas chromatography to have essentially the composition of the water/cyclobutanone azeotrope (about 80% cyclobutanone in the combined aqueous and organic layers). At this point the column head temperature rose sharply to about 96.5°C as the remaining water was azeotropically removed from the still. Initially the distillate receiver formed two liquid phases, but by the end of collecting the second fraction the distillate returned to one liquid phase. A total of 34.5 g was collected as the second fraction. The second fraction contained about 5.7% water. A third fraction, 90.54 g, was collected while the head temperature remained at 96.5-96.7ºC. This product fraction [distillate (ii)] was found to comprise 99.95% cyclobutanone and 0.05% water by gas chromatography and trace amounts of cyclobutanol by GC-mass spectroscopy. No other impurities were identified. The column was allowed to cool and the residue in the still was collected for analysis. The residue [distillation residue (iii)] weighed 37 g and comprised approximately 96% cyclobutanone, 1% cyclobutanol and unquantified concentrations of ketals, ethers and other high boiling compounds.

EXAMPLE 9 - Diethanolamine-catalyzed aldehyde conversion

A 350 g sample of the organic layer from Example 4, containing approximately 88% cyclobutanone (CBON) and 0.56% cyclopropanecarboxaldehyde (CPCA), was mixed with 1.75 g of diethanolamine (DEA) in a jacketed glass round bottom flask. The contents of the flask were heated to 50°C with stirring and an inert nitrogen atmosphere. After a reaction period at this temperature of 7.5 hours, the material was sampled and heating was continued for an additional 15 hours. GC analysis of the material at this time indicated that 87.5% of the CPCA had been converted to high boiling aldehyde condensation oligomers and greater than 96.9% of the initial CBON remained intact. The flask was cooled to 15-20ºC and 3.5 g of Amberlyst 15 ion exchange resin in hydrogen form was added with stirring. The material was kept at 15-20ºC for 4 hours then filtered to remove the resin. When 1 ml of the filtered liquid reached 24 When kept at 90ºC for 12 hours, very little cyclobutane was lost, indicating that virtually all of the DEA had been removed by the resin treatment.

EXAMPLE 10 - Diethanol-catalyzed aldehyde conversion

A 100 g sample of the organic layer from Example 4, containing about 88% cyclobutanone (CBON) and 0.56% cyclopropanecarboxaldehyde (CPCA), was mixed with 0.51 g diethanolamine (DEA) in a jacketed glass round bottom flask. The flask was held at 60°C under an inert nitrogen atmosphere for 7.5 hours. A sample of the material was removed, then cooled to 50°C and held for an additional 14.5 hours. A second sample was removed and the flask was held at 50°C for an additional 24.5 hours. GC analysis of the material at this time showed that 100% of the CPCA had been converted to higher boiling aldehyde condensation oligomers. Greater than 91% of the initial CBON remained intact. The flask was cooled to 34ºC and 1.0 g of Amberlyst 15 ion exchange resin in hydrogen form was added with stirring. The material was held at 28ºC for 6.5 hours then filtered to remove the resin. The flask was then heated to 60ºC and held at that temperature for an additional 15 hours to check the stability of the CBON at higher temperatures. GC analysis showed no decrease in cyclobutanone concentration during the final hold period, indicating that virtually all of the DEA had been removed by the resin treatment.

EXAMPLE 11 - Aldehyde conversion by air oxidation

A 1 mL sample of the organic layer from Example 4 was stirred at 60°C in a 7.4 mL (0.25 ounce) sealed glass vial with air present in the headspace. After 16, 54.5, and 79.5 hours at 60°C, the material was sampled and analyzed. The amount of CPCA and CBON present in each sample was:

This example demonstrates that air oxidation under mild conditions is an effective method of destroying the aldehydes with little loss of cyclobutanone product. On a pure cyclobutanone basis, the CPCA concentration was reduced from 0.37 wt% to 0.043 wt%, which is well within the preferred aldehyde specifications.

EXAMPLE 12 - Diisopropylamine-catalyzed aldehyde conversion

Cyclobutanone (100 mL) with a GC analysis of > 99% cyclobutanone and 0.57% CPA was mixed with distilled water and allowed to separate into two liquid phases. The organic layer comprised 94.5% cyclobutanone, 5.86% water and 0.49% cyclopropylcarboxaldehyde. After decantation, approximately 1 mL of diisopropylamine was added to the organic layer. The mixture was heated to 60ºC, maintained at this temperature, and samples were taken and analyzed after 2, 6.7 and 28.7 hours of heating at 60ºC. The amount of CPCA and CBON present in each sample was:

The use of diisopropylamine resulted in significant destruction of CPCA with moderate losses of cyclobutanone.

EXAMPLE 13 - Diethanolamine-catalyzed aldehyde conversion

An organic product fraction prepared as described in Example 4 was mixed with an organic distillate layer prepared as described in Example 2. Approximately 37 kg of this material, containing 0.55% CPCA and >85% cyclobutanone, was mixed with 185 g of diethanolamine in a 22 L jacketed glass vessel and stirred at 50°C for 23 hours. The mixture was cooled to 20°C and 370 g of Amberlyst 15 ion exchange resin in hydrogen form was added. The mixture was stirred for 4 hours then filtered through a 0.45 µm filter. The CPCA concentration in the filtrate was found by GC analysis to be less than 0.05% with 95% of the initial cyclobutanone remaining intact.

EXAMPLE 14 - Step (5) Distillation

The purified material prepared in Example 13 was distilled using the procedure and equipment described in Example 5. The product fraction, weighing 34.7 kg, was analyzed by GC and found to contain 99.73% cyclobutanone, 0.1% water, less than 0.05% cyclopropanecarboxaldehyde, and no detectable cyclobutanol or cyclopropanemethanol.

EXAMPLE 15 - Step (5) distillation with added solvent

This example demonstrates the use of an inert azeotrope-forming solvent in the final dehydration and purification of the cyclobutanone. An organic phase (271.6 g) obtained by the procedure described in Example 7 was introduced into a 2 L still of a batch distillation apparatus along with 831.8 g of methyl tert-butyl ether (MTBE). The distillation apparatus consisted of a 2.54 cm (1 inch) i.d. vacuum-jacketed glass column packed with 1 m (40 inches) of 3.2 mm (1/8 inch) Penn State packing. The column was equipped with a liquid divider head, a reflux timer, a cooling water condenser, a distillate receiving flask, an electric heating mantle, a nitrogen line, and a dry ice cold trap. After a steady state boiling equilibrium was reached at total reflux, the reflux timer was set to 20% withdrawal and distillate collection was started. An initial distillate fraction was collected at a column head temperature of 50.6ºC to 51.9ºC. This material separated into two liquid phases in the receiving flask and was found by gas chromatography to have a composition of essentially the water/MTBE azeotrope, about 3% water total. As the water content of the still fell below the azeotropic composition, the head temperature gradually rose to 54ºC as nearly pure MTBE was withdrawn from the head. The column head temperature rose rapidly to 95.8-96.8ºC as the last traces of MTBE were distilled from the pot. When the temperature stabilized at 96.8ºC, the product fraction was collected. Distillation was terminated when the pot contents were reduced to about 50 g and the level was well below the thermocouple in the still. The average purity of the product fraction was 99.8% cyclobutanone, < 0.03% MTBE and < 0.1% water. The bubble residue was 99.7 wt.% cyclobutanone.

Example 16 - Step III and IV distillations using a pressure difference

This example illustrates the operation of Stage III and Stage IV distillations using pressure differentials. A process simulator was used to model a continuous two-column pressure differential distillation sequence. The Stage III distillation was simulated as a column consisting of 30 theoretical stages, with 15 stages above the feed point, operating at 1034 Torr (0.138 MPa) with a reflux ratio of 3. The Stage N distillation was simulated as a column consisting of 20 theoretical stages, with 7 stages above the feed point, operating at 5170 Torr (0.69 MPa) with a reflux ratio of 2.5. The fresh feed to the first column was fed at a rate of 200 kg-moles per hour with a composition as shown in Table II. The distillate from the step N distillation column was recycled to the feed of the step III distillation column, while the distillate from the step III distillation column was fed to the step N distillation column. Water and cyclobutanol were removed from the bottom of the column as column underflow from the step III distillation column and the cyclobutanone product was removed as column underflow from the step IV distillation column. The results of the simulation are given in Table II, where the molar flows are kg-mol/hour and the step N distillate is recycled to step III. TABLE II

Claims (13)

1. A process for obtaining cyclobutanone with a purity of at least 90 wt.% from a crude product mixture comprising cyclobutanone, water and a plurality of other organic compounds resulting from the oxidation of cyclobutanol in water, by means of the steps comprising: (1) distilling the crude product mixture to obtain (1) a distillate comprising cyclobutanone, water, cyclopropane methanol, cyclobutanol, 3-buten-1-ol, 2-buten-1-ol, cyclopropane carboxaldehyde, ethers and mixed ethers of cyclobutanol, cyclopropane methanol, 3-buten-1-ol and 2-buten-1-ol and hemiketals of cyclopropane methanol, 3-buten-1-ol and 2-buten-1-ol with cyclobutanone; and (ii) a distillation residue comprising water, metal salts and high boiling organic compounds; (2) allowing the distillate from step (1) to separate into (i) an organic phase comprising a minor amount of the cyclobutanone contained in the distillate and a major amount of impurities that are less soluble in water than cyclobutanone; and (ii) an aqueous phase comprising water, a major amount of the cyclobutanone contained in the distillate and a minor amount of more hydrophilic impurities; (3) distilling the aqueous phase from step (2) to obtain (i) a minor amount of distillate comprising low boiling azeotropes comprising water and organic impurities in the aqueous phase, (ii) a major portion of distillate comprising an azeotrope of water and cyclobutanone, and (iii) a distillation residue comprising water, cyclopropanecarboxylic acid, γ-butyrolactone, cyclobutanol, cyclopropanemethanol, mixed ethers of alcohols and ketals formed from reactions between ethers and alcohols; (4) Allowing the distillate (ii) from step (3) to separate into (i) a cyclobutanone-rich organic phase comprising cyclobutanone, water and near boiling aldehydes, and (ii) separating an aqueous phase comprising cyclobutanone and water; and (5) distilling the organic phase (1) from step (4) to obtain (1) a first distillate comprising an azeotrope of water and cyclobutanone, (ii) a second distillate comprising cyclobutanone having a purity of at least 90%, and (iii) a distillation residue comprising cyclobutanol, cyclopropane methanol, mixed ethers of alcohols and ketals formed from reactions between ethers and alcohols. 2. The process of claim 1, wherein the crude product mixture distilled in step (1) comprises 2 to 20 wt.% cyclobutanone, 70 to 97 wt.% water, and 0.2 to 10 wt.% impurities; the concentration of cyclobutanone in the condensed distillate from step (1) is 4 to 12 wt.%; the distillation column of step (3) has at least 15 equilibrium stages; the distillation column of step (5) has at least 12 equilibrium stages; and the second distillate (ii) from step (5) comprises cyclobutanone having a purity of at least 95%. 3. A process according to claim 1, in which the organic phase (i) from step (2) is extracted with water using a weight ratio of water:organic phase of 1:4 to 5:1 and the aqueous extract phase is combined with the aqueous phase (ii) from step (2). 4. A process according to claim 1, in which the organic phase (i) of step (4) is contacted with a molecular oxygen-containing gas or a base in order to convert aldehydes present into high-boiling compounds. 5. Process according to claim 4, in which the organic phase is brought into contact with air at a temperature of 20 to 80°C. 6. Process according to claim 4, in which the organic phase is contacted with a secondary or tertiary amine at a temperature of 20 to 80°C. 7. The process of claim 1 wherein step (5) is conducted in the presence of a high boiling solvent that (1) has a boiling point of at least 30°C above the boiling point of cyclobutanone; (2) does not form a binary azeotrope with cyclobutanone; (3) does not form a binary azeotrope with alcohol impurities that has a boiling point within 10°C of the boiling point of pure cyclobutanone; and (4) does not react with cyclobutanone. 8. A process according to claim 7, wherein the high boiling inert solvent has a boiling point of 140 to 200°C and is selected from straight and branched chain alkanes and alkyl esters of alkanoic acids. 9. The process of claim 1 wherein step (5) is conducted in the presence of an added organic azeotrope-forming solvent which (1) forms a heterogeneous minimum boiling binary azeotrope with water or a heterogeneous minimum boiling ternary azeotrope with water and cyclobutanone which is the lowest boiling of all binary azeotropes and pure components in the ternary system; (2) does not react with cyclobutanone; and (3) does not form a binary azeotrope with alcohol impurities which has a boiling point within 10°C of the boiling point of pure cyclobutanone. 10. The process of claim 9, wherein the added azeotrope-forming solvent is selected from aliphatic, cycloaliphatic and aromatic hydrocarbons containing up to 7 carbon atoms; aliphatic, aromatic and cyclic ethers containing up to 6 carbon atoms; aliphatic and cycloaliphatic or aromatic nitriles containing up to 5 carbon atoms; and aliphatic and cycloaliphatic ketones containing up to 6 carbon atoms; aliphatic and cycloaliphatic halogenated hydrocarbons containing up to 6 carbon atoms and up to 3 chlorine, 6 fluorine or 3 bromine atoms; and aliphatic and cycloaliphatic carboxylic acid esters containing up to 5 carbon atoms. 11. A process according to claim 9, wherein the added azeotrope-forming solvent is selected from methyl tert-butyl ether, tert-amyl ether, ethyl acetate, isopropyl acetate, n-pentane, n-hexane, cyclohexane, methyl isopropyl ketone, 1-chlorobutane and 2-chlorobutane. 12. A process for obtaining cyclobutanone having a purity of at least 90 wt.% from a crude product mixture comprising cyclobutanone, water and a plurality of other organic compounds resulting from the oxidation of cyclobutanol in water, by means of the steps comprising: I. Distilling the crude product mixture to produce (1) a distillate comprising cyclobutanone, water, cyclopropane methanol, cyclobutanol, 3-buten-1-ol, 2-buten-1-ol, cyclopropane carboxaldehyde, ethers and mixed ethers of cyclobutanol, cyclopropane methanol, 3-buten-1-ol and 2-buten-1-ol and hemiketals and ketals of cyclopropane methanol, cyclobutanol, 3-buten-1-ol and 2-buten-1-ol with cyclobutanone; and (ii) to obtain a distillation residue comprising water, metal salts and high boiling organic compounds such as γ-butyrolactone, cyclopropanecarboxylic acid and hemiketals and ketals of cyclopropanemethanol, cyclobutanol, 3-buten-1-ol and 2-buten-1-ol with cyclobutanone; II. Allowing the resulting mixture to separate into (i) an organic phase comprising a minor amount of cyclobutanone contained in the distillate and a major amount of impurities less soluble in water than cyclobutanone, such as ethers, ketals and colored bodies; and (ii) an aqueous phase comprising water, a major amount of the cyclobutanone contained in the distillate, a minor amount of more hydrophilic impurities such as alcohols and cyclopropanecarboxaldehyde; III. distilling the aqueous phase from step II at a pressure in the range of 100 to 2000 torr to obtain (1) a distillate comprising an azeotrope of water and cyclobutanone and (ii) a column underflow product comprising water, cyclopropanecarboxylic acid, γ-butyrolactone, cyclobutanol, cyclopropanemethanol, mixed ethers of alcohols and ketals formed from reactions between ethers and alcohols; and IV. Distilling the distillate (i) from step III at a pressure of 2000 to 6000 Torr to obtain (i) a distillate product containing an azeotrope of water and cyclobutanone and added to the feeds of the distillation of step III, and (ii) obtaining a column underflow product comprising cyclobutanone having a purity of at least 90%; provided that the distillation of step IV is conducted at a pressure that is at least 760 Torr greater than the pressure at which step III is operated. 13. The process of claim 12, wherein step III is operated at a pressure of 700 to 1250 Torr and step IV is operated at a pressure of 3500 to 5500 Torr, provided that the operating pressure of step IV is at least 2280 Torr greater than the operating pressure of step III.